1. Field of the Invention
The present invention relates to a lean combustion gas engine which is useful mainly as a driving source for a stationary-type electrical power facility for industrial or commercial use. This application is based on patent applications No. Hei 10-132371 and No. Hei 10-228416 filed in Japan, the contents of which are incorporated herein by reference.
2. Relevant Art
In recent years, more attention has been paid towards lean combustion gas engines, due to their low pollution properties. The main trend is for conventional lean combustion gas engines to take the form of the precombustion chamber-type model, which uses spark plugs as the ignition source; however, dual fuel engines are known to function as the aforementioned as well. The latter type of engine performs the combustion of gas fuel by means of injecting a pilot fuel (liquid) directly into the main combustion chamber in the amount of approximately 5.about.15% of the entire heating amount, and uses this pilot fuel as the ignition source. More concretely, a small amount of pilot fuel is injected from the main fuel injection valve of a standard diesel engine in order to achieve the aforementioned ignition. It is also achieved by the injection of 100% liquid fuel from the main fuel injection valve to switch in a diesel operation from in a gas operation.
However, when combusting a lean mixture using a conventional spark plug-equipped precombustion chamber-type gas engine, unless a strong ignition energy is generated, fluctuation of the combustion with misfire occurs In addition, when comparing this process with that performed by the diesel engine with an identical cylinder bore, the aforementioned process is advantageous from the standpoint of low pollution with a NOx concentration of approximately one-tenth the latter, however, the aforementioned process is also disadvantageous from the standpoint of exhibiting a low engine thermal efficiency.
With regard to improving the combustion fluctuation, in order to ensure a dependable combustion within the precombustion chamber, numerous research is being conducted into measures for optimizing the spark plug position within the precombustion chamber, and for creating a uniform distribution of the fuel-air mixture within the aforementioned precombustion chamber. However, since neither of the above increases the ignition energy, there exist limits with regard to improving the engine thermal efficiency and combustion fluctuation.
On the other hand, in the case of a gas mode operation of conventional dual fuel engines, disadvantages that the exhaust amount of the NOx concentration and the soot and dust are increasing, at increasing the pilot fuel to improve the engine thermal efficiency and suppress the combustion fluctuation, such that the advantageous low pollution (low CO.sub.2) properties of the gas engine cannot be exploited Meanwhile, in the case of reducing the amount of the pilot fuel, at the cranking speed (approximately 150.about.200 rpm) at the time of starting the engine, it is not possible to sufficiently raise the fuel pump ejection pressure, and the pressure is unable to exceed the injection-valve opening pressure, such that fuel injection is not possible. Consequently, another mechanism is required for starting the gas engine which uses the pilot fuel as the ignition source.